Hereinafter, a conventional single-crystal manufacturing apparatus based on the Czochralski method will be explained by exemplifying growing a silicon single crystal.
FIG. 6 shows a schematic sectional view of an example of the conventional single-crystal manufacturing apparatus.
In the single-crystal manufacturing apparatus 101 used for manufacturing a silicon single crystal based on the CZ method, there are generally arranged crucibles 109 and 110 that contain a raw material melt 106 and are movable upwardly and downwardly, and a heater 111 that is arranged so as to surround the crucibles 109 and 110, inside a main chamber 105 where the single crystal is grown. A pulling chamber 107 for accommodating and taking out the grown single crystal is continuously provided above the main chamber 105. In the case of manufacturing a single crystal by using the single-crystal manufacturing apparatus 101 as described above, a seed crystal 113 is dipped in the raw material melt 106 and gently pulled upwardly with being rotated to grow a rod-shaped single crystal 108, while the crucibles 109 and 110 are moved upwardly according to the growth of the crystal so that a melt surface is always maintained at a constant height in order to obtain a desired diameter and desired crystal quality.
When the single crystal 108 is grown, after the seed crystal 113 attached to a seed holder 114 is dipped in the raw material melt 106, a wire 115 is gently wound up with being rotated in a desired direction with a pulling mechanism (not shown) to grow the single crystal 108 at an end portion of the seed crystal 113.
In this case, a pulling rate for a constant diameter portion having a constant diameter of the single crystal 108 is extremely slow, for example, approximately 0.4 to 2.0 mm/min, depending on the diameter of the single crystal to be pulled. If it is pulled fast by constraint, the single crystal during the growth is deformed, and consequently a cylindrical product having a constant diameter can be no longer obtained. Otherwise, there arise problems such that slip dislocations are generated in the single crystal 108, the single crystal 108 cannot be a product by being detached from the melt and the like. Thus, increasing a crystal growth rate has been limited.
However, for the purpose of improving productivity and reducing cost in the foregoing manufacture of the single crystal 108 based on the CZ method, the increase in the growth rate of the single crystal 108 is one main method, and accordingly various improvements have hitherto been made in order to achieve the increase in the growth rate of the single crystal 108.
It has been known that the growth rate of the single crystal 108 is determined by heat balance of the single crystal 108 during growth and can be increased by efficiently removing the heat emitted from a surface of the single crystal. In the case, an enhancement of a cooling effect on the single crystal 108 enables the single crystal to be further efficiently manufactured. Furthermore, it has been known that crystal quality is varied depending on a cooling speed of the single crystal 108. For example, Grown-in defects formed in the silicon single crystal during the growth of the single crystal can be controlled by a ratio of the pulling rate (the growth rate) of the single crystal to a temperature gradient in the crystal, and a defect-free single crystal (a single crystal of N-region) can be grown by controlling this (See Japanese Unexamined Patent publication (Kokai) No. H11-157996). Thus, the enhancement of the cooling effect on a single crystal during growth is important for manufacturing the defect-free single crystal and for improving productivity by increasing the growth rate of the single crystal.
As a method for enhancing the cooling effect, there is proposed a structure that comprises a gas flow-guide cylinder 103 for flow-guiding an inert gas and a heat-insulating ring 104 for intercepting direct heat radiation from the heater and the raw material melt to the gas flow-guide cylinder 103 (See Japanese Unexamined Patent publication (Kokai) No. S64-65086). In this method, a heat-insulating effect by the heat-insulating ring and the cooling effect of the inert gas on the single crystal can be expected.
Moreover, there is disclosed a single-crystal manufacturing apparatus provided with a large heat-insulating means around a single crystal to improve the heat-insulating effect (See Japanese Patent No. 3634867).
There is also disclosed a gas flow-guide cylinder that allows observing a shape of the single crystal during growth by providing the gas flow-guide cylinder with a quartz window plate, in addition to the above-described effect of the gas flow-guide cylinder (See Japanese Unexamined Patent publication (Kokai) No. H3-97688). However, the purpose of the quartz window plate is to observe the crystal or optical measurement for controlling a diameter thereof, and it is not involved in the viewpoint concerning the cooling effect.